1. Field of the Invention
The present invention relates generally to a radio communication system and a radio transmitter in multi-carrier code-division multiple access (CDMA) radio communication, and more particularly to such a radio communication system and a radio transmitter which correct errors caused by retransmissions.
2. Description of the Related Art
In a retransmission control system in conventional multi-carrier communication, a mobile station and a base station execute the following processes (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-104574). The mobile station measures receiving channel qualities at every subcarrier or at every subcarrier group to transmit the channel qualities to the base station. The mobile station requests a retransmission to the base station if there is an error in received data received from the base station. The base station receives the request for the retransmission to transmit retransmission data to the mobile station. At this time, the base station uses a subcarrier other than a subcarrier or a subcarrier group which are determined not to be used, based on the receiving channel qualities to transmit the retransmission data.
However, there is the problem that the above-mentioned conventional technique requires a large overhead to feed back information about a channel response status and a subcarrier to be used to a transmission side. There is the problem that system throughput in communication should be improved and processing amount for retransmission control and channel response estimation should be reduced.